/* Jacobi.f -- translated by f2c (version of 20 August 1993  13:15:44).
   You must link the resulting object file with the libraries:
	-lf2c -lm   (in that order)
*/

#include "f2c.h"

/* Table of constant values */

static real c_b2 = (float)1.;
static integer c__1 = 1;
static real c_b13 = (float)-1.;


/* Subroutine */ int jacobi_(n, b, x, work, ldw, iter, resid, matvec, info)
integer *n;
real *b, *x, *work;
integer *ldw, *iter;
real *resid;
/* Subroutine */ int (*matvec) ();
integer *info;
{
    /* System generated locals */
    integer work_dim1, work_offset, i__1;

    /* Local variables */
    static integer temp;
    extern /* Subroutine */ int matsplit_();
    extern doublereal snrm2_();
    static integer i, maxit;
    extern /* Subroutine */ int scopy_(), saxpy_();
    static integer x1, mm;
    static real tol;


/*  -- Iterative template routine -- */
/*     Univ. of Tennessee and Oak Ridge National Laboratory */
/*     October 1, 1993 */
/*     Details of this algorithm are described in "Templates for the */
/*     Solution of Linear Systems: Building Blocks for Iterative */
/*     Methods", Barrett, Berry, Chan, Demmel, Donato, Dongarra, */
/*     Eijkhout, Pozo, Romine, and van der Vorst, SIAM Publications, */
/*     1993. (ftp netlib2.cs.utk.edu; cd linalg; get templates.ps). */

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */
/*     .. Function Arguments .. */

/*  Purpose */
/*  ======= */

/*  JACOBI solves the linear system Ax = b using the Jacobi iterative */
/*  method. The matrix splitting should be accomplished before calling */
/*  this routine. The diagonal elements of the matrix must be passed into 
*/
/*  this routine in the first column of matrix WORK. */

/*  Relative error measured: norm( X - X_1 ) / norm( X ). */

/*  Arguments */
/*  ========= */

/*  N       (input) INTEGER */
/*          On entry, the dimension of the matrix. */
/*          Unchanged on exit. */

/*  B       (input) REAL array, dimension N */
/*          On entry, right hand side vector B. */
/*          Unchanged on exit. */

/*  X       (input/output) REAL array, dimension N. */
/*          On input, the initial guess. This is commonly set to */
/*          the zero vector. */
/*          On exit, if INFO = 0, the iterated approximate solution. */

/*  WORK    (workspace) REAL array, dimension (LDW,3) */
/*          Workspace for residual, direction vector, etc. */

/*  LDW     (input) INTEGER */
/*          The leading dimension of the array WORK. LDW >= max(1,N). */

/*  ITER    (input/output) INTEGER */
/*          On input, the maximum iterations to be performed. */
/*          On output, actual number of iterations performed. */

/*  RESID   (input/output) REAL */
/*          On input, the allowable convergence measure for */
/*          norm( x - x_1 ) / norm( x ). */
/*          On output, the final value of this measure. */

/*  MATVEC  (external subroutine) */
/*          The user must provide a subroutine to perform the */
/*          matrix-vector product */

/*               y := alpha*A*x + beta*y, */

/*          where alpha and beta are scalars, x and y are vectors, */
/*          and A is a matrix. Vector x must remain unchanged. */
/*          The solution is over-written on vector y. */

/*          The call is: */

/*             CALL MATVEC( ALPHA, X, BETA, Y ) */

/*          The matrix is passed into the routine in a common block. */

/*  INFO    (output) INTEGER */

/*          =  0: Successful exit. Iterated approximate solution returned.
 */

/*          >  0: Convergence to tolerance not achieved. This will be */
/*                set to the number of iterations performed. */

/*          <  0: Illegal input parameter, or breakdown occurred */
/*                during iteration. */

/*                Illegal parameter: */

/*                   -1: matrix dimension N < 0 */
/*                   -2: LDW < N */
/*                   -3: Maximum number of iterations ITER <= 0. */

/*  BLAS CALLS:   SAXPY, SCOPY, SNRM2 */
/*  ========================================================== */

/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. External Routines .. */

/*     .. */
/*     .. Executable Statements .. */

    /* Parameter adjustments */
    work_dim1 = *ldw;
    work_offset = work_dim1 + 1;
    work -= work_offset;
    --x;
    --b;

    /* Function Body */
    *info = 0;

/*     Test the input parameters. */

    if (*n < 0) {
	*info = -1;
    } else if (*ldw < max(1,*n)) {
	*info = -2;
    } else if (*iter <= 0) {
	*info = -3;
    }
    if (*info != 0) {
	return 0;
    }

    maxit = *iter;
    tol = *resid;

/*     Alias workspace columns. */

    mm = 1;
    x1 = 2;
    temp = 3;

    *iter = 0;

/*     Form matrix splitting inv(M) and N. */

    matsplit_(&c_b2, &b[1], &work[mm * work_dim1 + 1], ldw, "JACOBI", "SPLIT",
	     6L, 5L);

L10:

/*        Perform Jacobi iteration */

    ++(*iter);

/*        Save the current approximation to X in X1. */

    scopy_(n, &x[1], &c__1, &work[x1 * work_dim1 + 1], &c__1);

/*        Apply iteration; result is updated approximation vector x. */

    scopy_(n, &b[1], &c__1, &work[temp * work_dim1 + 1], &c__1);
    (*matvec)(&c_b2, &x[1], &c_b2, &work[temp * work_dim1 + 1]);
    i__1 = *n;
    for (i = 1; i <= i__1; ++i) {
	x[i] = work[i + mm * work_dim1] * work[i + temp * work_dim1];
/* L15: */
    }

/*        Compute error and check for acceptable convergence. */

    saxpy_(n, &c_b13, &x[1], &c__1, &work[x1 * work_dim1 + 1], &c__1);
    *resid = snrm2_(n, &work[x1 * work_dim1 + 1], &c__1) / snrm2_(n, &x[1], &
	    c__1);

    if (*resid <= tol) {
	goto L30;
    }
    if (*iter == maxit) {
	goto L20;
    }

    goto L10;

L20:

/*     Iteration fails */

    *info = 1;
    goto L30;

L30:

/*     Iteration successful. Reconstruct matrix A. */

    matsplit_(&c_b2, &b[1], &work[mm * work_dim1 + 1], ldw, "JACOBI", "RECON\
STRUCT", 6L, 11L);

    return 0;

/*     End of JACOBI */

} /* jacobi_ */